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Verb. The act of hitting the back of another persons knee when their knee is locked, causing the person to stumble and possibly fall. There is also the muthasucka twofer where when you perform the act, the individual yells out in surprise, "muthasucka!".
"Man, when he muthasucka'd me I almost fell down those stairs! Imma muthasuck the shit out of him tomorrow!"
by Arfdawg March 16, 2011